Positive electrode material for a lithium ion accumulator

Abstract

A compound of formula Li_1+x(Ni_aMn_bCo_cAl_y)_1−xO₂ wherein:

a, b and c are non-zero;

a+b+c+y=1;

1.05≦(1+x)/(1−x)≦1.25;

0.015≦y(1−x);

the atomic amount of manganese representing from 95% to 100% of the atomic amount of nickel.

Description

FIELD OF THE INVENTION[0001]The technical field of the invention is that of electrochemically active materials used in the manufacturing of positive electrodes (or cathodes) of rechargeable electrochemical generators (or accumulators) with lithium.PRIOR ART[0002]Lithiated oxides of transition metals are known as an active cathode material which may be used in lithium rechargeable generators. In the positive electrode, lithiated oxides of transition metals of general formula LiMO2 are generally used as an electrochemically active material, wherein M is most often Mn, Ni or Co, and their substituted derivatives. For example, as an active cathode material, mention may be made of the compound Li(Ni0.8Co0.15Al0.05)O2, which is a lithiated oxide of nickel-cobalt-aluminium. This material, further called NCA (nickel-cobalt-aluminium), is present in the positive electrode of lithium rechargeable generators used for industrial application, such as electric hybrid vehicles and space applicatio...

AI Technical Summary

Benefits of technology

[0024]The compound, object of the invention, has higher electrochemical capacity than that of the materials of the prior art while retaining good heat stability. This material has good electrochemical power performances at 30° C. and at −20° C.

Problems solved by technology

This type of active material however does not have sufficient heat stability.

Indeed, in the case of overloading or accidental short-circuiting of the generator, a significant and sudden rise in temperature occurs, due to an exothermic reaction of the active material with the electrolyte.

Given that most materials have a very unstable structure, overheating causes degradation of these active materials.

Insufficient heat stability of these positive electrode materials poses a safety problem when they are used in small generators intended to provide strong currents (power elements).

However, the electrochemical capacity of the materials described in this document is insufficient.

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